So under that law, energy from coal-fired plants that went up in North Dakota since '07 can't be sold to Minnesotans.

North Dakota and three electric co-ops with Minnesota customers filed a federal lawsuit in 2011. They argued that Minnesota is basically trying to regulate utilities in other states. The court agreed with them, saying the Constitution makes it clear that only Congress can make rules about interstate commerce.

North Dakota Attorney General Wayne Stenehjem applauded the appeals court ruling, saying in a statement: "North Dakota has once again prevailed in its lawsuit against Minnesota’s overreaching regulations.”

Stenehjem noted that Minnesota is also on the hook to cover North Dakota's court costs, which he says are up to about $1 million.

Gov. Dalrymple says if Minnesota energy regulators require utilities to pay more to burn coal it will hamper North Dakota's growing lignite industry, which already provides a large share of Minnesota's electric power. Regulators here imposed higher costs on coal-burners as part of a plan to require utilities to generate a quarter of their energy from renewable sources by 2024.